An interferometric measuring device, normally referred to as a white-light interferometer, is described in published German patent document DE 101 31 778, in which the basic method of functioning of such a white-light interferometer is also described. In the case of this known interferometric measuring device, a short coherent light source is used to generate light in a customary manner, the light of the short coherent light source being split up by a beam splitter into an object beam guided via an object light path and a reference beam guided via a reference light path. The object surface to be measured is imaged on an image pick-up, e.g. a CCD camera, and superposed by the reference wave formed by the reference beam. The depth scanning may be implemented by moving a reference element that reflects the reference beam, or moving the object, relative to the measuring device. When the object is moved, the image plane of the objective and the reference plane are in the same plane. During depth scanning, the object remains fixed in the field of view of the CCD camera, and the object is only moved relative to the reference plane along the depth axis (z-direction). In this manner, measurements of industrial surfaces, for example, may be conducted with a depth resolution in the range of a few nanometers. The panorama optics and the objective described in this published German patent document also allow a measurement in narrow and deep bores, using a 360° circumferential picture of a nearly radially symmetric object, which means that valve seats, for example, may be completely measured. However, it is difficult for this interferometric measuring device to measure guide bores completely.
An interferometric measuring device suitable for deep and narrow bores and based on the principle of white light interferometry is described in published German patent document DE 100 15 878, an intermediate image being generated by the objective taking the form of an endoscope, and intermediate-image scanning being carried out for the depth scanning. During the depth scanning, the object remains fixed in the field of view of the image pick-up or the CCD camera. Using this known measuring device, it is difficult to completely measure a guide bore and, in addition, a valve seat as well.
Furthermore, it is also known that a readily accessible object surface can be measured by a so-called lateral scanning white-light interferometer, as described in A. Olszak, “Lateral scanning white-light interferometer,” Applied Optics, Vol. 39, 3907-3913, 2000. In this connection, the reference plane is inclined at an angle to the object surface. For depth scanning, the object is moved laterally through the field of view of the objective in such a manner that a relative change in the optical path length between the reference light path and the object light path, i.e. between the reference arm and the object arm, results for each object point. In the case of the lateral movement, the correlogram resulting from the lateral movement is recorded and evaluated for each object point. Spatially extended objects and moving objects can be measured by this device. A measurement in narrow and deep bores, however, is not possible with this device.
An object of the present invention is to facilitate measurement of deep and narrow bores or, for example, valve seats in a rapid and reliable manner.